Three energy firms are to pay a total of £10.5m following August’s power cut that left over a million people without electricity and caused travel chaos.
RWE Generation, which runs Little Barford Power Station, and Orstead, which runs Hornsea offshore wind farm, will each pay £4.5m to the UK energy watchdog’s redress fund.
Distributor company UK Power Networks has agreed to pay £1.5m.
Ofgem says it will continue to look into the role National Grid played.
More than a million people lost power during the cut in August, which affected homes, businesses and transport.
The lights went out just before 17:00 BST on Friday 9 August, causing blackouts across the Midlands, the South East, South West, North West and North East of England, and Wales.
While the power cut lasted for less than an hour, problems on the rail network carried on over the weekend.
Energy watchdog Ofgem launched its investigation in August.
It found that after a lightning strike, Hornsea offshore wind farm and Little Barford Power Station both went down.
Jonathan Brearley, Ofgem’s incoming chief executive, told the BBC’s Today programme that the simultaneous outage was an “exceptional event”.
He said the equipment within the generators should have “ridden through” the lightning strike and it should not have resulted in a countrywide power failure.
Mr Brearley said the Ofgem report recommended three sets of actions for UK energy companies.
The part of National Grid that gives Britain power needs to be set up “the right way”, new forms of generation – such as wind power – need to be a more secure source of supply, and, Mr Brearley added, “if we do ever have to disconnect people we want to make sure we protect our critical infrastructure and the most vulnerable”.
National Grid says that it has begun its own review and will update an industry standards panel in April.
In a statement, it said it would work with regulators and “colleagues across the industry, to address the issues raised and make sure that lessons are learned, and any changes made are in the best interests of the consumer”.
Hornsea One, which operated the wind power station that went down, said in a statement that it took the interruption “very seriously”.
“We have co-operated with Ofgem throughout their investigations and conducted a thorough internal review of the events in order to prevent a situation like this from happening again,” it said.
Business and Energy Secretary Andrea Leadsom said: “The disruption caused to people and businesses by the power cut in August was unacceptable. However, customers can be confident that we have one of the most robust energy systems in the world and today’s report will help us reduce the risks of it happening again and ensure our energy sector is better prepared in the future.”
Although power was out for less than an hour, essential services such as hospitals experienced disruption when their safety systems reacted to voltage fluctuations affecting the network.
Some of the power companies began to switch services back on for customers before they were certain that this would not shut down power to other parts of the grid.
Thameslink trains that had only been added to the fleet in 2014 suffered a software glitch from systems sensitive to power fluctuation.
Though some trains could be re-started, many required an engineer to travel out to where the train was stranded for a manual restart.
London’s Underground service also saw station power interrupted and signalling was lost.
Four hospitals were also affected by the cut. While two were able to switch to back-up generators, two saw their back-up generators fail.